Acoustic wave resonator

ABSTRACT

An acoustic wave resonator includes a resonating part disposed on and spaced apart from a substrate by a cavity, the resonating part including a membrane layer, a first electrode, a piezoelectric layer, and a second electrode that are sequentially stacked. 0 Å≤ΔMg≤170 Å may be satisfied, ΔMg being a difference between a maximum thickness and a minimum thickness of the membrane layer disposed in the cavity.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No. 15/788,062 filed on Oct. 19, 2017 which claims the benefit under 35 USC § 119(a) of Korean Patent Application No. 10-2017-0036738 filed on Mar. 23, 2017, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND 1. Field

The present disclosure relates to an acoustic wave resonator.

2. Description of Related Art

Recently, as wireless communications devices have become smaller and smaller, methods of miniaturizing radio frequency component technologies has been actively sought. An example of the miniaturization of the radio frequency component technology includes a bulk acoustic wave (BAW) resonator type filter produced using a semiconductor thin film wafer.

The bulk acoustic wave (BAW) resonator refers to a thin film type element implemented as a filter, where the thin film type element induces resonance. In forming the thin film type element, a piezoelectric dielectric material is deposited on a silicon wafer, and a semiconductor substrate is included. The resonance of the thin film type element utilizes piezoelectric characteristics of the piezoelectric dielectric material.

Fields of application of the bulk acoustic wave (BAW) resonator include small, lightweight filters, oscillators, resonance elements, acoustic wave resonance mass sensors, and the like, and may be included in mobile communications devices, chemical and biological devices, and the like.

Research into structural shapes and other ways for increasing performance characteristics of the bulk acoustic wave resonator is ongoing, and, thus, research into a method of manufacturing the bulk acoustic wave resonator having increased performance characteristics is also ongoing.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In one general aspect, an acoustic wave resonator includes a resonating part disposed on and spaced apart from a substrate by a cavity, the resonating part including a membrane layer, a first electrode, a piezoelectric layer, and a second electrode that are sequentially stacked. 0 Å≤ΔCg≤340 Å may be satisfied, ΔCg being a difference between a maximum gap and a minimum gap of the cavity.

0 Å≤ΔMg≤170 Å may be satisfied, ΔMg being a difference between a maximum thickness and a minimum thickness of the membrane layer disposed in the cavity.

The resonating part may further include a resonance active region disposed on the cavity, the first electrode and the second electrode may each include connection electrodes extended outside the resonance active region, and the cavity may include at least one opening connected to the outside. 30 μm≤Ra/Hw≤200 μm may be satisfied, Ra being an area (μm²) of the resonance active region, and Hw being a total length (μm) of the at least one opening.

A width of each of the connection electrodes may be greater than or equal to 60 μm.

The at least one opening may be formed between the membrane layer and the substrate.

The total length of the at least one opening may be greater than or equal to a total width of the connection electrodes.

The substrate may include an etch stop layer disposed on a surface thereof, and the cavity may be disposed between the etch stop layer and the membrane layer.

The etch stop layer may include a same material as the membrane layer.

In one general aspect, an acoustic wave resonator includes a resonance active region spaced apart from a substrate by a cavity, the resonance active region comprising a membrane layer, a first electrode, a piezoelectric layer, and a second electrode sequentially stacked on the cavity, and at least one opening formed in an outer portion of the cavity connecting the cavity with the outside. 30 μm≤Ra/Hw≤200 μm is satisfied, Ra being an area (μm²) of the resonance active region, and Hw being a total length (μm) of the at least one opening.

The acoustic wave resonator of claim 10, may further include respective connection electrodes extending to the outside of the resonance active region from the first electrode and the second electrode, a width of each of the connection electrodes being greater than or equal to 60 μm.

The total length of the at least one opening may be equal to or greater than a total width of the connection electrodes.

The acoustic wave resonator may further include a cavity layer interposed between the substrate and the resonance active region. The cavity may be disposed in the cavity layer.

The acoustic wave resonator may further include an etching stop part disposed in the cavity layer and disposed along an edge of the cavity.

Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating an example of an acoustic wave resonator.

FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1 .

FIG. 3 is a cross-sectional view taken along a line II-II′ of FIG. 1 .

FIGS. 4, 5, 6, 7, and 8 are views illustrating an example of a method for manufacturing an acoustic wave resonator.

FIG. 9 is an enlarged view of a part A of FIG. 2 .

FIG. 10 is a graph illustrating an effect of the acoustic wave resonator illustrated in FIG. 1 .

FIG. 11 is a graph illustrating an example of a ripple component of FIG. 10 .

FIG. 12 is a view illustrating a change in the ripple component according to a change in Ra/Hw.

FIG. 13 is a schematic cross-sectional view illustrating an example of an acoustic wave resonator.

FIG. 14 is a schematic circuit diagram illustrating an example of a filter.

FIG. 15 is a schematic circuit diagram illustrating an example of a filter.

Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent after an understanding of the disclosure of this application. For example, the sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent after an understanding of the disclosure of this application, with the exception of operations necessarily occurring in a certain order. Also, descriptions of features that are known in the art may be omitted for increased clarity and conciseness.

The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided merely to illustrate some of the many possible ways of implementing the methods, apparatuses, and/or systems described herein that will be apparent after an understanding of the disclosure of this application.

Throughout the specification, when an element, such as a layer, region, or substrate, is described as being “on,” “connected to,” or “coupled to” another element, it may be directly “on,” “connected to,” or “coupled to” the other element, or there may be one or more other elements intervening therebetween. In contrast, when an element is described as being “directly on,” “directly connected to,” or “directly coupled to” another element, there can be no other elements intervening therebetween.

As used herein, the term “and/or” includes any one and any combination of any two or more of the associated listed items.

Although terms such as “first,” “second,” and “third” may be used herein to describe various members, components, regions, layers, or sections, these members, components, regions, layers, or sections are not to be limited by these terms. Rather, these terms are only used to distinguish one member, component, region, layer, or section from another member, component, region, layer, or section. Thus, a first member, component, region, layer, or section referred to in examples described herein may also be referred to as a second member, component, region, layer, or section without departing from the teachings of the examples.

Spatially relative terms such as “above,” “upper,” “below,” and “lower” may be used herein for ease of description to describe one element's relationship to another element as shown in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, an element described as being “above” or “upper” relative to another element will then be “below” or “lower” relative to the other element. Thus, the term “above” encompasses both the above and below orientations depending on the spatial orientation of the device. The device may also be oriented in other ways (for example, rotated 90 degrees or at other orientations), and the spatially relative terms used herein are to be interpreted accordingly.

The terminology used herein is for describing various examples only, and is not to be used to limit the disclosure. The articles “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “includes,” and “has” specify the presence of stated features, numbers, operations, members, elements, and/or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, members, elements, and/or combinations thereof.

Due to manufacturing techniques and/or tolerances, variations of the shapes shown in the drawings may occur. Thus, the examples described herein are not limited to the specific shapes shown in the drawings, but include changes in shape that occur during manufacturing.

The features of the examples described herein may be combined in various ways as will be apparent after an understanding of the disclosure of this application. Further, although the examples described herein have a variety of configurations, other configurations are possible as will be apparent after an understanding of the disclosure of this application.

FIG. 1 is a plan view of an example of an acoustic wave resonator, FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1 , and FIG. 3 is a cross-sectional view taken along a line II-II′ of FIG. 1 .

Referring to FIGS. 1 and 2 , an example of an acoustic wave resonator 100 includes a substrate 110 and a resonating part 120.

A cavity C is formed between the substrate 110 and the resonating part 120. The resonating part 120 is formed on a membrane layer 150 and is spaced apart from the substrate 110 by the cavity C.

The substrate 110 is a substrate including stacked silicon. For example, as the substrate 110, a silicon wafer is used, or a silicon-on-insulator (SOI) type substrate is used.

The substrate 110 includes etch stop layer 115. The etch stop layer 115 is disposed on one surface of the substrate 110, and may prevent the substrate 110 from being etched by etching gas when the cavity C is formed during the manufacturing of the acoustic wave resonator.

The etch stop layer 115 may be formed of silicon nitride (SiN) or silicon oxide (SiO2). Additionally or alternatively, the etch stop layer may be formed of the same material as a membrane layer 150 to be described below.

The resonating part 120 includes a first electrode 121, a piezoelectric layer 123, and a second electrode 125. The resonating part 120 is formed by sequentially stacking the first electrode 121, the piezoelectric layer 123, and the second electrode 125. Therefore, the piezoelectric layer 123 is disposed between the first electrode 121 and the second electrode 125.

Since the resonating part 120 is formed on the membrane layer 150, the membrane layer 150, the first electrode 121, the piezoelectric layer 123, and the second electrode 125 are sequentially stacked on the substrate 110.

The membrane layer 150, together with the substrate 110, forms the cavity C. The membrane layer 150 is formed along a surface of a sacrificial layer 131 (described below), and may form the cavity C together with the substrate 110 by removing the sacrificial layer 131. Therefore, the membrane layer 150 may be formed of a material which is not easily removed during the forming of the cavity C.

For example, in a case in which halide-based etching gases such as fluorine (F), chlorine (Cl), or the like is used to remove a portion (e.g., a cavity region) of the cavity layer 140, the membrane layer 150 is formed of a material having low reactivity with the above-mentioned etching gases. In this case, the membrane layer 150 may be formed of a dielectric layer containing any one of silicon nitride (SiN), silicon oxide (SiO₂), manganese oxide (MgO), zirconium oxide (ZrO₂), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO₂), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and zinc oxide (ZnO), or any one of aluminum (Al), nickel (Ni), chromium (Cr), platinum (Pt), gallium (Ga), and hafnium (Hf). However, these materials are merely exemplary, and the configuration is not limited thereto.

The first electrode 121 and the second electrode 125 may be formed of a metal such as gold, molybdenum, ruthenium, iridium, aluminum, platinum, titanium, tungsten, palladium, chromium, nickel, or the like, or alloys of these metals, but is not limited thereto.

The piezoelectric layer 123 partially covers the first electrode 121.

As a material of the piezoelectric layer 123, zinc oxide (ZnO), aluminum nitride (AlN), doped aluminum nitride, lead zirconate titanate, quartz, or the like may be selectively used. The doped aluminum nitride may further include a rare earth metal or a transition metal. As an example, the rare earth metal may include one or more of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). The transition metal may include one or more of hafnium (Hf), titanium (Ti), zirconium (Zr), and magnesium (Mg).

The resonating part 120 as described above includes a resonance active region S including the first electrode 121, the piezoelectric layer 123, and the second electrode 125. The resonance active region S may be a region from which a resonance substantially occurs by vibration of the piezoelectric layer 123, Thus, in FIGS. 1-3 , the resonance active region S is defined as a region positioned over the cavity C and disposed in a contour of a frame 170.

The resonating part 120 is spaced apart from the substrate 110 by the cavity C. This configuration may improve a quality factor (Q factor).

The cavity C is formed between the resonating part 120 and the substrate 110. This configuration may prevent acoustic waves generated in the piezoelectric layer 123 from being affected by the substrate 110.

In addition, reflective characteristics of the acoustic wave generated in the resonating part 120 may be improved by the cavity C. Since the cavity C is an empty space and has an impedance close to infinity, the acoustic wave may remain in the resonating part 120 without being lost or deteriorated by the cavity C.

The frame 170 is disposed on an upper portion of the resonating part 120.

The frame 170 may be formed in a ring shape along an edge of the resonating part 120. However, the shape of the frame 170 is not limited thereto, and may also be formed as discontinuous arcs.

The acoustic wave resonator 100 may prevent energy loss of an elastic wave by using the frame 170 to reflect a horizontal direction elastic wave radiated toward an outside of the resonating part 120 to an inside of the resonating part 120. In this configuration, since the horizontal direction elastic wave reduces energy loss, the acoustic wave resonator 100 may have a high Q-factor (kt2).

The high Q-factor may increase the blocking of other frequency bands in implementing a filter or a duplexer, and high kt2 may secure a bandwidth to increase data transmission amount and speed at the time of transmitting and receiving data.

The frame 170 may be formed of a piezoelectric material, a dielectric material, or a metal. For example, the frame 170 may be formed of one of aluminum nitride (AlN), lead zirconate titanate (PZT), silicon oxide (SiO₂), titanium oxide (TiO₂), molybdenum (Mo), gold (Au), titanium (Ti), copper (Cu), tungsten (W), and aluminum (Al), or a synthetic material having any one thereof as a main component.

The first electrode 121 and the second electrode 125 each include connection electrodes 121 a and 125 a extended to the outside of the resonating part 120, and a first connecting electrode 180 and a second connecting electrode 190 is connected to the respective connection electrodes 121 a and 125 a.

The first connecting electrode 180 and the second connecting electrode 190 may be external connecting terminals for confirming characteristics of the resonator and the filter. However, the first connecting electrode 180 and the second connecting electrode 190 are not limited thereto.

In addition, a metal frame 180 a formed along a periphery of the first electrode 121 is formed on the first electrode 121.

The metal frame 180 a is bonded to the first electrode 121, and penetrates a protective layer 127 to be exposed to the outside.

As shown in FIGS. 1-3 , the metal frame 180 a extends from the first connecting electrode 180, and may be formed together with the first connecting electrode 180 in an operation of forming the first connecting electrode 180. However, the metal frame 180 a is not limited thereto, and may also be spaced apart from the first connecting electrode 180 and may also be manufactured by a different operation from the first connecting electrode 180.

The protective layer 127 is disposed along a surface of the acoustic wave resonator 100, and may protect the acoustic wave resonator 100 from the outside. In this case, the first connecting electrode 180 and the second connecting electrode 190 are exposed to the outside of the protective layer 127. Therefore, the protective layer 127 is disposed along a surface formed by the remaining elements except for the first connecting electrode 180 and the second connecting electrode 190.

The protective layer 127 may be formed of one insulating material of silicon oxide based insulating material, silicon nitride based insulating material, and aluminum nitride based insulating material, but is not limited thereto. The protective layer 127 may be provided to perform frequency trimming.

The acoustic wave resonator configured as described above includes at least one opening P in which the cavity C is opened to the outside. As illustrated in FIG. 1 , openings P are disposed in all directions along a contour of the cavity C, and may be used as inlets through which the etching gas is introduced into the cavity C in an operation of manufacturing the cavity C.

The opening P may be formed between the membrane layer 150 and the substrate 110 (e.g., the etch stop layer 115). In addition, the opening P may be formed to expand the cavity C along a surface direction of the cavity C.

Therefore, the opening P may be formed in a side portion or an upper portion of the cavity C and may be formed to have approximately the same gap as a gap of the cavity C.

A method for manufacturing an acoustic wave resonator, such as the one shown in FIG. 1 , will be described hereinafter.

FIGS. 4 through 8 are views illustrating an example of a method for manufacturing an acoustic wave resonator.

First, referring to FIG. 4 , the etch stop layer 115 may be formed on the substrate 110.

The etch stop layer 115 may serve to protect the substrate 110 when the sacrificial layer 131 is removed to form the cavity C (FIG. 1 ). The etch stop layer 115 may be formed of silicon nitride (SiN), silicon oxide (SiO₂), or the like, but is not limited thereto.

The sacrificial layer 131 may be then formed on the etch stop layer 115.

The sacrificial layer 131 may be removed by a subsequent etching operation to form the cavity C (FIG. 1 ). Therefore, the sacrificial layer 131 may be formed of a material such as polysilicon, polymer, or the like that may be easily etched. However, the material of the sacrificial layer 131 is not limited thereto.

In this operation, the sacrificial layer 131 is also be formed on a region in which the opening P (FIG. 1 ) is formed. Referring to FIG. 4 , the sacrificial layer 131 may have a reduced thickness toward an outer portion. The sacrificial layer 131 formed in the opening P may have the same or similar thickness as the central portion. Accordingly, even though various elements are stacked on the sacrificial layer 131 in subsequent manufacturing operations, a state in which a side surface or a top surface of the sacrificial layer 131, formed in the opening P, is exposed to the outside may be maintained.

The membrane layer 150 is then formed on the sacrificial layer 131. The membrane layer 150 positioned on the cavity C serves to maintain a shape of the cavity C and support the resonance active region S (see FIG. 1 ).

As described above, the membrane layer 150 may be formed of a dielectric layer containing one or more of silicon nitride (SiN), silicon oxide (SiO₂), manganese oxide (MgO), zirconium oxide (ZrO₂), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO₂), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and zinc oxide (ZnO), or one or more of aluminum (Al), nickel (Ni), chromium (Cr), platinum (Pt), gallium (Ga), and hafnium (Hf). However, the material of the membrane layer 150 is not limited thereto.

Next, as illustrated in FIG. 5 , the first electrode 121 and the piezoelectric layer 123 may be sequentially formed on the membrane layer 150.

The first electrode 121 may be formed by depositing a conductive layer on the membrane layer 150 and then removing (e.g., patterning) an unnecessary portion. The piezoelectric layer 123 may be formed by depositing a piezoelectric material on the first electrode 121.

The first electrode 121 may be formed of a molybdenum (Mo) material. However, the material of the first electrode 121 is not limited thereto, and may include various metals such as gold, ruthenium, iridium, aluminum, platinum, titanium, tungsten, palladium, chromium, nickel, and/or the like, or their alloys.

In addition, the piezoelectric layer 123 may be formed of aluminum nitride (AlN). However, the material of the piezoelectric layer 123 is not limited thereto, and may be formed of various piezoelectric materials such as doped aluminum nitride, zinc oxide (ZnO), lead zirconate titanate, quartz, and the like. The doped aluminum nitride may further include a rare earth metal or a transition metal. As an example, the rare earth metal includes one or more of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). The transition metal may include one or more of hafnium (Hf), titanium (Ti), zirconium (Zr), and magnesium (Mg).

Next, as illustrated in FIG. 6 , the second electrode 125 may be formed on the piezoelectric layer 123. According to the present exemplary embodiment, the second electrode 125 may be formed of molybdenum (Mo). However, the material of the second electrode 125 is not limited thereto, and may be formed of various metals such as gold, ruthenium, iridium, aluminum, platinum, titanium, tungsten, palladium, chromium, nickel, and the like.

In addition, during this operation, the frame 170 may be formed along a periphery of the second electrode 125. The frame 170 is formed in an outer portion of the second electrode and has a thickness thicker than that of the second electrode 125.

The frame 170 may be formed of the same material as the second electrode 125, but is not limited thereto.

Next, as illustrated in FIG. 7 , an unnecessary portion of the piezoelectric layer 123 is removed, and the protective layer 127 is formed along a surface of the resonating part 120. The piezoelectric layer 123 may be removed by a photolithography operation. The piezoelectric layer 127 may be formed of one insulating material of silicon oxide based insulating material, silicon nitride based insulating material, and aluminum nitride based insulating material, but is not limited thereto.

Next, the connection electrodes 121 a and 125 a (see FIG. 2 ) are exposed by partially removing the protective layer 127, and the first and second connecting electrodes 180 and 190. The metal frame 180 a is then formed on the connection electrodes 121 a and 125 a.

The first connecting electrode 180 and the metal frame 180 a may be formed by depositing gold (Au), copper (Cu), or the like on the first electrode 121. Similarly, the second connecting electrode 190 may be formed by depositing gold (Au), copper (Cu), or the like on the second electrode 125.

Next, as illustrated in FIG. 8 , the cavity C may be formed.

The cavity may be formed by removing the sacrificial layer 131 illustrated in FIG. 7 , and consequently, the acoustic wave resonator 100 illustrated in FIG. 1 may be completed. The sacrificial layer 131 may be removed by an etching method.

In a case in which the sacrificial layer 131 is formed of a material such as polysilicon, polymer, or the like, the sacrificial layer 131 may be removed by a dry etching method using a halide-based etching gas (e.g., XeF₂) such as fluorine (F), chlorine (Cl), and the like. Therefore, the sacrificial layer 131 may be in contact with the halide-based etching gas supplied through the opening P, and may be removed from a portion positioned in the opening P.

The cavity C of the acoustic wave resonator configured as described above may have a gap difference between a central portion and a peripheral portion.

FIG. 9 is an enlarged view of a part A of FIG. 2 . Referring to FIG. 9 , the cavity C of the acoustic wave resonator may have a gap g1 of the central portion of the cavity C narrower than a gap g2 of the peripheral portion of the cavity C, and accordingly, the cavity C may have a form in which the gap is increased from the central portion to the peripheral portion.

Such a gap difference may be formed by a thickness deviation (ΔMg, ΔSg) of the membrane layer 150 and/or the substrate 110.

The cavity C may be formed by removing the sacrificial layer 131 as described above. Therefore, since a portion of the membrane layer 150 or the substrate 110 (e.g., the etch stop layer) together with the sacrificial layer 131 may be removed in the operation of removing the sacrificial layer 131, the above-mentioned thickness deviation (ΔMg, ΔSg) may occur.

FIG. 10 is a graph illustrating an effect of the acoustic wave resonator illustrated in FIG. 1 and FIG. 11 is a graph illustrating a ripple component of FIG. 10 .

First, referring to FIG. 11 , a ripple component may refer to magnitude (peak to peak) of a ripple appearing at an inflection point of a graph illustrating characteristics of the acoustic wave resonator according a frequency band.

Therefore, as the ripple component is decreased, performance of the acoustic wave resonator may be improved, and as the ripple component is increased, the performance of the acoustic wave resonator may be deteriorated.

FIG. 10 is a table and a graph illustrating results obtained by measuring ripple components of the acoustic wave resonator having various thickness deviations. In a case in which the thickness deviation of the membrane layer 150 is increased in the acoustic wave resonator, the ripple component is also increased.

Here, the thickness deviation of the membrane layer 150 may refer to a difference between a maximum thickness and a minimum thickness of the membrane layer 150 disposed in the cavity C.

In addition, it may be seen from the graph that when the thickness deviation of the membrane layer 150 exceeds 170 Å, the ripple component is rapidly increased.

As such, in an example of the acoustic wave resonator described above with reference to FIGS. 1-3 , the thickness deviation of the membrane layer may be in the range of 170 Å or less. Accordingly, in the acoustic wave resonator according to the present exemplary embodiment, the thickness deviation of the membrane layer 150 may be expressed as in Equation 1 below 0 Å≤ΔMg≤170 Å  (Equation 1) where ΔMg is a difference between a maximum thickness and a minimum thickness of the membrane layer disposed in the cavity.

Here, a lower limit may refer to a case in which the membrane layer 150 is not removed at all during the operation of removing the sacrificial layer 131.

The membrane layer 150 may be formed on the surface of the sacrificial layer 131. In a case in which polysilicon (Si) is used as the sacrificial layer 131, a thickness deviation of about 10 Å may occur on the surface of the sacrificial layer 131 due to roughness of a surface of polysilicon (Si).

Thereby, the membrane layer 150 stacked on the sacrificial layer 131 may have a thickness deviation up to about 10 Å due to roughness of the surface of the sacrificial layer 131. In this case, a lower limit of the thickness deviation of the membrane layer 150 may be defined to 10 Å. However, the lower limit of the thickness deviation of the membrane layer 150 is not limited thereto.

During removal of the sacrificial layer 131, a portion of the etch stop layer 115 of the substrate 110 may also be removed together with the membrane layer 150, and as a result, the thickness deviation ΔSg may also occur on the substrate 110 as illustrated in FIG. 9 .

In a case in which the etch stop layer 115 is formed of the same material as the membrane layer 150, the same amount of the etch stop layer 115 as that of the membrane layer 150 may be removed. Therefore, the thickness deviation ΔSg of the etch stop layer 115 may be limited to the same range as Conditional Equation 1 above.

Thereby, the cavity of the acoustic wave resonator according to the present exemplary embodiment may satisfy Equation 2 in relation to deviations (ΔCg, ΔSg+ΔMg) of the gap. 0 Å≤ΔCg≤340 Å  (Equation 2) where ΔCg may refer to a difference between the maximum gap g2 and the minimum gap g1 of the cavity.

The acoustic wave resonator 100 shown in FIGS. 1-3 , for example, may limit a size of the opening P into which the etching gas is introduced to significantly decrease the thickness deviation of the membrane layer 150.

In a case in which the size of the opening P is increased, a rate at which the etching gas which may be introduced into the cavity C may be increased. Therefore, the sacrificial layer 131 may be removed in a shorter time than a structure having a small opening P, and as a result, the etching of the membrane layer 150 or the etch stop layer 115 may be significantly decreased.

Referring to FIG. 1 , the openings P may be disposed along the contour of the cavity C. However, the openings P may be formed in a tunnel form from the resonance active region S to the contour of the cavity C, and both ends of the tunnel may have approximately the same size and shape. Therefore, it may be understood that the openings P are disposed along the outer portion of the resonance active region S.

As illustrated in FIG. 1 , since the resonance active region S has the connection electrodes 121 a and 125 a connected to both sides thereof, the openings P may be formed only in the remaining portion except for the portions on which the connection electrodes 121 a and 125 a are disposed among an outer portion of the resonance active region S.

A width of the connection electrodes 121 a and 125 a may have a lower limit defined to approx. 60 μm. Since the acoustic wave resonator 100 has two connection electrodes 121 a and 125 a, approx. 120 μm of the periphery of the resonance active region S may be used to dispose the connection electrodes 121 a and 125 a.

Therefore, an overall periphery of the resonance active region S may be 120 μm or more to accommodate connection electrodes 121 a and 125 a.

Since the overall periphery of the resonance active region S is increased as an area of the resonance active region S, the opening P may also be formed to be large. Therefore, referring to in FIG. 1 , the size of the opening P may be numerically limited based on a ratio of the area of the resonance active region and the length of the opening P.

The acoustic wave resonator 100 may satisfy Equation 3 below in relation to the size of the opening P. 30 μm≤Ra/Hw≤200 μm  (Equation 3)

Here, Ra may refer to an area (μm²) of the resonance active region S, and Hw may refer to an overall length (μm) of the openings P. The area of the resonance active region S may refer to an overall area of the resonance active region S illustrated on a plane of the acoustic wave resonator illustrated in FIG. 1 , and the length of the openings P may refer to the overall length of the openings P formed along the contour of the cavity C.

Therefore, the reduction in Ra/Hw indicates that the overall length of the openings P is increased and the openings P are formed along an overall periphery of the resonance active region S except for the connection electrodes 121 a and 125 a.

Referring to FIG. 1 , four openings P may be included in the acoustic wave resonator 100. Therefore, Hw may be defined as a sum of lengths (L1, L2, L3, and L4) of the respective openings P.

For example, in a case in which the overall periphery of the resonance active region S is 400 μm (for convenience of calculation, it is assumed that the resonance active region S having a square shape of which one side has a length of 100 μm is formed), and the width of the connection electrode is 60 μm, a maximum length in which the openings P may be formed may be limited to 280 μm. In this case, since the area of the resonance active region S is 10000 μm², Ra/Hw of 35.7 μm may be calculated. Therefore, it may be seen that Ra/Hw is included in the range of Equation 3.

In a case in which the overall periphery of the resonance active region S is 240 μm (for convenience of calculation, it is assumed that the resonance active region S having a square shape of which one side has a length of 60 μm is formed), and the width of the connection electrode is 60 μm, the maximum length in which the openings P may be formed may be limited to 120 μm. In this case, since the area of the resonance active region S is 3600 μm2, Ra/Hw of 30 μm may be calculated. Therefore, Ra/Hw of the above example may also be included in the range of Equation 3, and it may be seen that Ra/Hw of the present example is a lower limit value of Equation 3.

In a case in which the overall length (L1+L2+L3+L4) of the openings P is shorter than an overall width of the connection electrodes 121 a and 125 a, Ra/Hw may be 30 μm or more. Therefore, when the overall length (L1+L2+L3+L4) of the openings P is the same as or greater than the overall width of the connection electrodes 121 a and 125 a, Ra/Hw may be included in the range of Equation 3.

Since the lower limit value of Equation 3 is a value derived by limiting the overall width of the connection electrodes 121 a and 125 a to 120 μm, when the widths of the connection electrodes 121 a and 125 a are changed, the lower limit value may also be changed.

FIG. 12 is a view illustrating a change in the ripple component according to a change in Ra/Hw, and illustrates results obtained by measuring the change in the ripple component according to the change in Ra/Hw while constantly maintaining the area of the resonance active region S in a table and a graph.

Referring to FIG. 12 , it may be seen that as a value of Ra/Hw is decreased, the ripple component is also decreased. In addition, referring to the graph, it may be seen that when the value of Ra/Hw is increased to 200 μm or more, the ripple component is sharply increased as illustrated in the graph.

Therefore, the acoustic wave resonator described above may define 200 μm, which is a limit point at which Ra/Hw is relatively and linearly increased, as an upper limit value of Ra/Hw.

The acoustic wave resonator described above may be capable of significantly decreasing the ripple component to increase resonance performance. Specifically, the thickness deviation between the membrane layer and the etch stop layer may be limited, and to this end, the length of the opening may be limited.

Since the sacrificial layer may be rapidly removed as the length of the opening is increased, the removal of the membrane layer and the etch stop layer together with the sacrificial layer may be significantly reduced, whereby gap deviation of the cavity may be reduced.

FIG. 13 is a schematic cross-sectional view illustrating another example of an acoustic wave resonator.

Referring to FIG. 13 , an acoustic wave resonator 200 may be a bulk acoustic wave resonator (BAW), and may include the substrate 110, the cavity layer 140, and the resonating part 120.

The substrate 110 is a substrate including stacked silicon. For example, as the substrate 110, a silicon wafer may be used, or a silicon-on-insulator (SOI) type substrate may be used as the substrate 110.

The substrate 110 includes the etch stop layer 115 including silicon nitride (SiN) or silicon oxide (SiO₂). The etch stop layer 115 is disposed on one surface of the substrate 110, and may prevent the substrate 110 from being etched by the etching gas when the cavity C is formed during the manufacturing of the acoustic wave resonator.

The cavity layer 140 is formed on the substrate 110, and the cavity C and an etching stop part 145 are disposed in the cavity layer 140.

The cavity C is formed as an empty space, and may be formed by removing a portion of the cavity layer 140.

Since the cavity C is formed in the cavity layer 140, the resonating part 120 formed on the cavity layer 140 is generally flat.

The etching stop part 145 is disposed along an edge of the cavity C. The etching stop part 140 may prevent the cavity C from being etched beyond a cavity region. Therefore, a horizontal region of the cavity C may be defined by the etching stop part 145.

The membrane layer 150 is formed on the cavity layer 140 to define a vertical region of the cavity C together with the substrate 110. Therefore, the membrane layer 150 may also be formed of a material which is not easily removed in an operation of forming the cavity C.

For example, in a case in which halide-based etching gases such as fluorine (F), chlorine (Cl), and the like are used to remove a portion (e.g., a cavity region) of the cavity layer 140, the membrane layer 150 may be formed of a material having low reactivity with the above-mentioned etching gases. In this case, the membrane layer 150 may be formed of a dielectric layer containing a material such as silicon nitride (SiN), silicon oxide (SiO₂), manganese oxide (MgO), zirconium oxide (ZrO₂), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO₂), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), or zinc oxide (ZnO), or a material such as aluminum (Al), nickel (Ni), chromium (Cr), platinum (Pt), gallium (Ga), or hafnium (Hf). However, the configuration is not limited thereto.

The resonating part 120 includes the first electrode 121, the piezoelectric layer 123, and the second electrode 125. The resonating part 120 is formed by sequentially the first electrode 121, the piezoelectric layer 123, and the second electrode 125. Therefore, the piezoelectric layer 123 is disposed between the first electrode 121 and the second electrode 125.

Since the resonating part 120 is formed on the membrane layer 150, the membrane layer 150, the first electrode 121, the piezoelectric layer 123, and the second electrode 125 are sequentially stacked on the substrate 110.

The resonating part 120 includes the resonance active region S formed by the first electrode 121, the piezoelectric layer 123, and the second electrode 125. The resonance active region S may be a region from which a resonance substantially occurs by vibrations of the piezoelectric layer 123. The resonance active region S is defined as a region positioned over the cavity C and disposed in a contour of a frame 170.

The first electrode 121 and the second electrode 125 may be formed of a metal such as gold, molybdenum, ruthenium, iridium, aluminum, platinum, titanium, tungsten, palladium, chromium, nickel, or the like, or alloys thereof, but is not limited thereto.

The piezoelectric layer 123 covers the first electrode 121.

As a material of the piezoelectric layer 123, zinc oxide (ZnO), aluminum nitride (AlN), doped aluminum nitride, lead zirconate titanate, quartz, or the like may be selectively used. The doped aluminum nitride may further include a rare earth metal or a transition metal. As an example, the rare earth metal may include one or more of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). The transition metal may include one or more of hafnium (Hf), titanium (Ti), zirconium (Zr), and magnesium (Mg).

The frame 170 is disposed on an upper portion of the resonating part 120.

The frame 170 may be formed in a ring shape along an edge of the resonating part 120. However, the form/shape of the frame 170 is not limited thereto, and may also be formed in a form discontinuous arcs.

The frame 170 may be formed of, for example, a piezoelectric material, a dielectric material, or a metal material. For example, the frame 170 may be formed of one or more of aluminum nitride (AlN), lead zirconate titanate (PZT), silicon oxide (SiO₂), titanium oxide (TiO₂), molybdenum (Mo), gold (Au), titanium (Ti), copper (Cu), tungsten (W), and aluminum (Al), or a synthetic material having any one thereof as a main component.

The protective layer 127 is disposed along a surface of the acoustic wave resonator 100, and may protect the acoustic wave resonator 100. The protective layer 127 is disposed along a surface formed by the second electrode 125 and the frame 170.

The protective layer 127 may be formed of one insulating material of silicon oxide based insulating material, silicon nitride based insulating material, and aluminum nitride based insulating material, but is not limited thereto.

The first electrode 121 and the second electrode 125 are formed extend outside of the piezoelectric layer 120, and are connected to the first connecting electrode 180 and the second connecting electrode 190, respectively.

The first connecting electrode 180 and the second connecting electrode 190 may be formed of metal materials such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), a copper-tin (Cu—Sn) alloy, alloys thereof, or the like.

The first connecting electrode 180 and the second connecting electrode 190 may be used as external connecting terminals for confirming characteristics of the resonator and the filter. However, the first connecting electrode 180 and the second connecting electrode 190 are not limited thereto.

The acoustic wave resonator according to the embodiment shown in FIG. 13 and described above may limit the range of the thickness deviation (ΔMg) of the membrane layer 150, the range of the gap deviation (ΔCg) of the cavity C, and the size of the opening by Equations 1 to 3 described above.

Hereinafter, an example of a filter including the bulk acoustic wave resonator described above will be described with reference to FIGS. 14 and 15 .

FIG. 14 is a schematic circuit diagram illustrating an example of a filter. Each of plural bulk acoustic wave resonators employed in the filter illustrated in FIG. 14 may be the acoustic wave resonator illustrated in FIG. 1 or 13 .

Referring to FIG. 14 , a filter 1000 is formed in a ladder type filter structure. Specifically, the filter 1000 includes a bulk acoustic wave resonators 1100 and 1200. A first bulk acoustic wave resonator 1100 may be connected in series between a signal input terminal to which an input signal RFin is input and a signal output terminal from which an output signal RFout is output, and a second bulk acoustic wave resonator 1200 may be connected between the signal output terminal and a ground.

FIG. 15 is a schematic circuit diagram illustrating an example of a filter. Each of the bulk acoustic wave resonators employed in the filter illustrated in FIG. 15 may be the acoustic wave resonator illustrated in FIG. 1 or 13 .

Referring to FIG. 15 , a filter 2000 is formed in a lattice type filter structure. Specifically, the filter 2000 includes bulk acoustic wave resonators 2100, 2200, 2300, and 2400 to filter balanced input signals RFin+ and RFin− to output balanced output signals RFout+ and RFout−.

As set forth above, according to the exemplary embodiments described above, the acoustic wave resonator may limit the gap deviation of the cavity to increase resonance performance, and may limit the length of the opening used to form the cavity for this purpose.

Since the sacrificial layer may be rapidly removed as the length of the opening is increased, the removal of the membrane layer together with the sacrificial layer may be significantly reduced, whereby the gap deviation of the cavity may be reduced.

While this disclosure includes specific examples, it will be apparent after an understanding of the disclosure of this application that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure. 

What is claimed is:
 1. An acoustic wave resonator, comprising: a resonance active region spaced apart from a substrate by a cavity, the resonance active region comprising a sequentially stacked first electrode layer, piezoelectric layer, and second electrode layer; a membrane layer, wherein a portion of the membrane layer forms an upper side portion of the cavity; and plural passages respectively connecting the cavity to an outside, each of the plural passages including a respective outside access to the outside, separated from a perimeter of the resonance active region, and a respective cavity access of the cavity at a periphery of the respective passage, each cavity access being a lateral opening disposed between the membrane layer and the substrate, a gap between the membrane layer and the substrate of each passage at the lateral opening being greater than a gap between the membrane layer and the substrate at a central portion of the cavity, wherein the membrane layer is continuously disposed from the portion of the membrane layer that forms the upper side portion of the cavity to an area outside of the periphery of the passages, and wherein the portion of the membrane layer includes a thickness deviation ΔMg, the thickness deviation ΔMg being a difference between a maximum layer thickness and a minimum layer thickness of the portion of the membrane layer, and where 0 Å<ΔMg<170 Å.
 2. The acoustic wave resonator of claim 1, further comprising respective connection electrodes, connecting to outside of the resonance active region, of the first electrode and the second electrode, wherein a total length of the respective cavity accesses along the perimeter of the resonance active region is greater than or equal to a total width of the respective connection electrodes along the periphery of the resonance active region.
 3. The acoustic wave resonator of claim 2, wherein the resonance active region has a polygonal shape, and the plural passages extend in respective directions away from the polygonal shape of the resonance active region.
 4. The acoustic wave resonator of claim 3, wherein the perimeter of the resonance active region has a square shape, and the total area (μm²) within the perimeter of the resonance active region is a square of a length (μm) of one side of the perimeter of the resonance active region.
 5. The acoustic wave resonator of claim 2, wherein the total width of the respective connection electrodes is greater than or equal to 120 μm.
 6. The acoustic wave resonator of claim 1, wherein 30 μm≤Ra/Hw≤200 μm is satisfied, Ra being a total area (μm²) within the perimeter of the resonance active region, and Hw being a total length (μm) of all of the respective cavity accesses along the perimeter of the resonance active region.
 7. The acoustic wave resonator of claim 6, wherein Ra/Hw is less than 175 μm.
 8. The acoustic wave resonator of claim 7, wherein Ra/Hw is greater than 125 μm and less than 160 μm.
 9. The acoustic wave resonator of claim 1, wherein ΔMg is greater than 10 Å.
 10. The acoustic wave resonator of claim 9, wherein ΔMg is less than 50 Å.
 11. The acoustic wave resonator of claim 9, wherein ΔMg is greater than 50 Å and less than 100 Å.
 12. The acoustic wave resonator of claim 1, wherein a layer portion of another layer forming a lower side of the cavity has corresponding layer thickness differences, where a difference between a maximum layer thickness and a minimum layer thickness of the layer portion of the other layer is ΔSg, and wherein a total of ΔMg and ΔSg is ΔCg, which meets the expression of 0 Å<ΔCg≤340 Å.
 13. The acoustic wave resonator of claim 12, wherein the other layer is an etch layer formed on the substrate or the other layer is the substrate.
 14. The acoustic wave resonator of claim 1, wherein ΔMg is greater than 100 Å.
 15. The acoustic wave resonator of claim 14, wherein ΔMg is less than or equal to 150 Å.
 16. The acoustic wave resonator of claim 1, further comprising a frame formed on the second electrode, and the perimeter of the resonance active region is within a perimeter of the frame.
 17. The acoustic wave resonator of claim 1, wherein the plural passages each respectively radiate outward from the respective cavity accesses in a direction toward a periphery of the cavity, with each of the respective outside accesses having a respective non-curved or curved opening length.
 18. The acoustic wave resonator of claim 1, wherein ΔMg is equal to or less than 100 Å.
 19. An acoustic wave resonator, comprising: a resonance active region spaced apart from a substrate by a cavity, the resonance active region comprising a sequentially stacked first electrode layer, piezoelectric layer, and second electrode layer; a membrane layer, wherein a portion of the membrane layer forms an upper side portion of the cavity; and one or more tunnels having respective cavity openings that are open to the outside at a periphery of the respective tunnel, the respective cavity openings being lateral openings disposed between the membrane layer and the substrate within the cavity, a gap between the membrane layer and the substrate of each tunnel at the lateral openings being greater than a gap between the membrane layer and the substrate at a central portion of the cavity, wherein the membrane layer is continuously disposed from the portion of the membrane layer that forms the upper side portion of the cavity to an area outside of the periphery of the one or more tunnels, and wherein the resonance active region has a polygonal shape, and the one or more tunnels extend in respective directions away from the polygonal shape of the resonance active region.
 20. The acoustic wave resonator of claim 19, wherein 30 μm≤Ra/Hw≤200 μm is satisfied, Ra being a total area (μm²) within a perimeter of the resonance active region, and Hw being a total length (μm) of all of the respective cavity openings along the perimeter of the resonance active region.
 21. The acoustic wave resonator of claim 20, wherein Ra/Hw is less than 175 μm.
 22. The acoustic wave resonator of claim 21, wherein Ra/Hw is less than 160 μm.
 23. The acoustic wave resonator of claim 22, wherein Ra/Hw is greater than 125 μm.
 24. The acoustic wave resonator of claim 19, wherein the portion of the membrane layer forming the upper side portion of the cavity has corresponding layer thickness differences, where a difference between a maximum layer thickness and a minimum layer thickness of the portion of the membrane layer is ΔMg, wherein 0 Å<ΔMg<170 Å.
 25. The acoustic wave resonator of claim 24, wherein ΔMg is greater than 10 Å.
 26. The acoustic wave resonator of claim 25, wherein ΔMg is less than 50 Å.
 27. The acoustic wave resonator of claim 24, wherein ΔMg is greater than 50 Å and less than 100 Å.
 28. The acoustic wave resonator of claim 19, wherein the portion of the membrane layer forming the upper side portion of the cavity has corresponding layer thickness differences, where a difference between a maximum layer thickness and a minimum layer thickness of the portion of the membrane layer is ΔMg, wherein a layer portion of another layer forming a lower surface of the cavity has corresponding layer thickness differences, where a difference between a maximum layer thickness and a minimum layer thickness of the layer portion of other layer is ΔSg, and wherein a total of ΔMg and ΔSg is represented by ΔCg, representing vertical gap deviations of the cavity, which meets the expression of 0 Å<ΔCg≤340 Å. 